This invention relates in general to communication systems, and more specifically to a method and apparatus for adaptively compensating for an inaccuracy in an analog-to-digital converter.
To reduce hardware expense and power consumption, a recent trend in communication receiver implementation has been to move the analog-to-digital (A/D) converter closer to the antenna. Communication systems, such as global positioning satellite (GPS) systems and cellular telephone systems, utilize multiple carriers within a single band. Receivers for such systems require high-performance A/D conversion, because high linearity is necessary to convert the multiple carriers. Without high linearity, self-interference is generated through cross product terms.
Unfortunately, the quantizers utilized in prior-art A/D converters have introduced gains and offsets that are not stable over time and temperature. These unstable gains and offsets have created unacceptable inaccuracy and non-linearity that render the prior-art A/D converters unusable for multiple-carrier conversion.
Thus, what is needed is a method and apparatus for adaptively compensating for an inaccuracy in an analog-to-digital converter. Preferably, the method and apparatus will provide quantizer gains and offsets that are sufficiently stable over time and temperature to produce the accuracy and linearity required for multiple-carrier A/D conversion.
An object of the present invention is to provide a method for adaptively compensating for an inaccuracy in an analog-to-digital converter. The method comprises comparing an analog input signal with a reference signal to generate a decision signal, and summing the analog input signal with a control value whose magnitude is determined by an accumulated value, and whose sign is determined by the decision signal, thereby generating an error signal. The method further comprises calculating a correlation value between the error signal and the decision signal, and accumulating the correlation value to produce the accumulated value, thereby adaptively compensating the inaccuracy.
Another object of the present invention is to provide an apparatus for adaptively compensating for an inaccuracy in an analog-to-digital converter. The apparatus comprises a comparator, coupled to an analog input signal and coupled to a reference signal for comparing the analog input signal with the reference signal to generate a decision signal. The apparatus further comprises a sign determiner, coupled to the comparator and coupled to an accumulator, for generating a control value whose magnitude is an accumulated value, and whose sign is determined by the decision signal. The apparatus also includes a summer coupled to the analog input signal and coupled to the sign determiner for summing the analog input signal with the control value, thereby generating an error signal, and a correlative multiplier coupled to the summer and coupled to the comparator for calculating a correlation value between the error signal and the decision signal. In addition, the apparatus includes the accumulator coupled to the correlative multiplier for accumulating the correlation value to produce the accumulated value, thereby adaptively compensating the inaccuracy.
A third object of the present invention is to provide an integrated circuit for adaptively compensating for an inaccuracy in an analog-to-digital converter. The integrated circuit comprises a comparator, intended to be coupled to an analog input signal and coupled to a reference signal for comparing the analog input signal with the reference signal to generate a decision signal. The integrated circuit further comprises a sign determiner, coupled to the comparator and coupled to an accumulator, for generating a control value whose magnitude is an accumulated value, and whose sign is determined by the decision signal. The integrated circuit also includes a summer intended to be coupled to the analog input signal and coupled to the sign determiner for summing the analog input signal with the control value, thereby generating an error signal, and a correlative multiplier coupled to the summer and coupled to the comparator for calculating a correlation value between the error signal and the decision signal. In addition, the integrated circuit includes the accumulator coupled to the correlative multiplier for accumulating the correlation value to produce the accumulated value, thereby adaptively compensating the inaccuracy.